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x(x-0.2)=640
We move all terms to the left:
x(x-0.2)-(640)=0
We multiply parentheses
x^2-0.2x-640=0
a = 1; b = -0.2; c = -640;
Δ = b2-4ac
Δ = -0.22-4·1·(-640)
Δ = 2560.04
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.2)-\sqrt{2560.04}}{2*1}=\frac{0.2-\sqrt{2560.04}}{2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.2)+\sqrt{2560.04}}{2*1}=\frac{0.2+\sqrt{2560.04}}{2} $
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